Breaking It Down: Bringing the Industrial Process a Little Closer to the Backyard

A piece of the 'green' bottle in the backyard compost pile after six weeks.  This photo was taken one week ago but could have been taken today.  The corn plastic remains unchanged.

A piece of the 'green' bottle in the backyard compost pile after six weeks. This photo was taken one week ago but could have been taken today. The corn plastic remains unchanged.

It’s Week Seven for our ‘green’ bottle in John’s backyard compost pile, and it remains unchanged. We asked Julie Muir, program manager of the Recycling Program at PSSI—the waste service that recently started a food-scrap composting program at Stanford University—to talk with us about industrial composting. Julie is also the president of the California Resource Recovery Association, making her especially qualified to discuss composting because several California cities are collecting compostable food scraps from homes and businesses.

Why did Stanford start a food scrap collection program?

By the early 2000s, the waste industry in California had established programs to recycle many components of the waste stream. We had done bottles and cans, we had done wood and paper, and we had done construction and demolition (C&D), so it was a natural progression. The next thing in the waste stream after C&D was food scraps. This came in conjunction with the fact that there were local facilities that could take food waste. Newby Island, a landfill in San Jose, was able to take food waste for composting.

We also did some research in the dining halls [of nearby colleges and universities]. When we found that over 50 percent of the trash from the dining halls was organic (meaning able-to-be-composted), we said “yeah this is the right thing to do.”

What happens at an industrial compost facility?

The compostables, including yard waste, apple cores, etc., are dumped on a pad and examined for contamination. Major contaminants will be pulled out, such as a plastic bag full of trash. Then the waste goes into a shredding machine that breaks the compostables down into small pieces. The shredded material is put into huge piles called windrows where it sits long enough to build up heat—a sign of healthy biodegradation. After a period of 90 to 180 days, the material goes through a trammel screen to sort out uniform-sized particles for finished product. Anything bigger (“the overs”) will go back into the pile. Corn plastics and other bioplastics are usually found in the overs since they do not degrade into small enough particles over 90 to 180 days.

What are some of the benefits and problems with food scrap collection, and are they being worked out?

People aren’t used to composting, and it has a bit of a “yuck factor.” Bottle and can recycling took a long time to become successful and profitable. Some people have criticized the food scrap collection programs in San Francisco and Toronto for being ineffective, but you have to have some realistic expectations starting out. You live, you work, and you play, sometimes in three different areas. People need to encounter composting everywhere for it to become a habit.

Check back with us in two weeks to learn what happens to our ‘green’ bottle in Week Nine, and we’ll also wrap up our discussion of backyard compost and corn plastic.

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